[arghwhat]

Note that not notifying the other party of changes could possibly be construed as fraud, depending on what legal system you are under.

But even when notified of the changes, the other party is quite likely to accept reasonable changes when they have a fully signed copy, as it is more convenient than pushing back...

[tialaramex]

If they don't want the signed contract back, that's the first time I've seen it. Every employer I worked for wanted the contract back with a signature. Newer ones were OK with an electronic (not digital, just pixels instead of ink) signature but they all wanted a signature.

When they get the modified contract back that's their notification of your adjusted terms. Is it polite to ask them to print a modified contract? Yes. But it may not always be practical.

[This is not legal advice, duh]

Because employer/ employee is asymmetric (unless you're literally hired by an individual) my understanding is that it is good sense for them to prefer your amended contract if the terms you wanted are acceptable, because the law in many places says if you have a take-it-or-leave-it contract then the person in the "take it or leave it" position, here the employee, is entitled to interpret any ambiguous provisions in the most advantageous way. Having amended the contract, you are now on equal footing with the employer and any remaining ambiguity is resolved equitably which means less risk of nasty surprises for them.

[arghwhat]

They of course need the signed contract back - all parties need a copy with all necessary signatures.

My point is that you should not sneak in changes with the signature. If the contract is changed, you should notify the parties of the changes, not pretend you just signed their copy. If you do not notify them, it might be seen as an attempt to trick the other parties.

How that would play out depends on your local legal system, with options ranging from "too bad", "contract or clause invalidated or reverted", all the way to "prosecuted for fraud".

"Your should just have expected me to have changed the contract and compared it with the previous version to find all the changes!" is not an argument that would get court approval up here...